1. Field of the Invention
The present invention relates generally to mechanical linkages, and in particular to a linkage for leveling a vegetable planter.
2. Description of the Prior Art
Mechanical linkages between tools, equipment and the like are well known and a variety of different designs have heretofore been devised to fulfill the requirements of particular applications. For example, many agricultural implements are designed for pulling by tractors and are connected thereto by mechanical linkages. A common type of tractor-mounted linkage is referred to in the industry as a three-point hitch and includes a laterally spaced pair of draft links and a center link positioned therebetween. The draft links are generally coupled to lifting arms which are raised and lowered by a rockshaft actuated by a hydraulic cylinder. The center link is generally adjustable so that the fore and aft pitch of the implement can be adjusted by the operator.
In operation, most tractor-drawn agricultural implements are repeatedly raised and lowered between transport positions above a ground surface and engaged work positions. Raising is accomplished with the aforementioned three-point hitch lifting arms. Implements are raised to their transport positions at the end of each pass through a field when the equipment must be turned around and when the equipment is transported from a storage area to a work area.
However, some implements are hinged for "floating" operation over uneven terrain and are susceptible to damage in their raised, transport positions. For example, the Model No. 33 vegetable planter manufactured by Deere & Company of Moline, Ill. includes a carriage assembly mounting a drive wheel at the front and a press wheel at the back. Such vegetable planters are generally mounted in even-numbered multiples on a transversely extending toolbar, which in turn is connected to a tractor three-point hitch.
The planter carriage is pivotally mounted and is adapted to rock fore and aft about a transverse pivotal axis between the drive and press wheels. Since each planter unit is thus adapted to float over uneven terrain, its drive and press wheels are maintained in continuous contact with a ground surface. However, when the planter is raised to its transport position the carriage generally rotates to a sloping orientation with its front drive wheel elevated and its rear press wheel lowered almost to the ground. In such a transport configuration the rear press wheel can engage the ground, and may in fact slide sideways along the ground if the tractor is turning with the rear press wheel engaged. Such lateral sliding is a frequent cause of planter damage. Hence, it is important to elevate the entire planter in its transport position enough so that its wheels do not contact the ground.
Another problem with such freely-tiltable planter units is that they include runner openers for depositing the seeds in the ground which tend to clog with dirt if the planter unit is tilted rearwardly when lowered. Furthermore, when the sloping carriage is lowered from its transport position to its work position, the rear press wheel can bounce upon impact and initiate harmful fore-and-aft rocking as the front and back wheels alternately bounce while the planter is lowered to the ground.
To overcome these problems, Deere & Company provides leveling spring attachments for preventing its Model No. 33 planters from tilting to the rear. However, a problem associated with the Deere & Company leveling spring attachment is that it remains in tension when the planter unit is in a work position which tends to lift or unload the rear press wheel. Insufficient down pressure on the rear press wheel can lead to poor soil compression over the newly planted seeds with lower crop yields as the ultimate result. The Deere & Company leveling spring attachment also tends to rapidly wear out the metal planter parts to which it is attached. The present invention addresses these problems with previous vegetable planters.